Re: [PATCH v7 2/6] KVM: arm64: Introduce pkvm_alloc_private_va_range()

[Marc Zyngier <maz@kernel.org>]

On Fri, 08 Apr 2022 21:03:25 +0100,
Kalesh Singh <kaleshsingh@google.com> wrote:
> 
> pkvm_hyp_alloc_private_va_range() can be used to reserve private VA ranges
> in the pKVM nVHE hypervisor. Allocations are aligned based on the order of
> the requested size.
> 
> This will be used to implement stack guard pages for pKVM nVHE hypervisor
> (in a subsequent patch in the series).
> 
> Credits to Quentin Perret <qperret@google.com> for the idea of moving
> private VA allocation out of __pkvm_create_private_mapping()
> 
> Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
> Tested-by: Fuad Tabba <tabba@google.com>
> Reviewed-by: Fuad Tabba <tabba@google.com>
> ---
> 
> Changes in v7:
>   - Add Fuad's Reviewed-by and Tested-by tags.
> 
> Changes in v6:
>   - Update kernel-doc for pkvm_alloc_private_va_range() and add
>     return description, per Stephen
>   - Update pkvm_alloc_private_va_range() to return an int error code,
>     per Stephen
>   - Update __pkvm_create_private_mapping to return an in error code,
>     per Quentin
>   - Update callers of __pkvm_create_private_mapping() to handle new
>     return value and params.
> 
> Changes in v5:
>   - Align private allocations based on the order of their size, per Marc
> 
> Changes in v4:
>   - Handle null ptr in pkvm_alloc_private_va_range() and replace
>     IS_ERR_OR_NULL checks in callers with IS_ERR checks, per Fuad
>   - Fix kernel-doc comments format, per Fuad
>   - Format __pkvm_create_private_mapping() prototype args (< 80 col), per Fuad
> 
> Changes in v3:
>   - Handle null ptr in IS_ERR_OR_NULL checks, per Mark
> 
> Changes in v2:
>   - Allow specifying an alignment for the private VA allocations, per Marc
> 
> 
>  arch/arm64/kvm/hyp/include/nvhe/mm.h |  6 ++-
>  arch/arm64/kvm/hyp/nvhe/hyp-main.c   | 18 ++++++-
>  arch/arm64/kvm/hyp/nvhe/mm.c         | 78 ++++++++++++++++++----------
>  3 files changed, 72 insertions(+), 30 deletions(-)
> 
> diff --git a/arch/arm64/kvm/hyp/include/nvhe/mm.h b/arch/arm64/kvm/hyp/include/nvhe/mm.h
> index 2d08510c6cc1..42d8eb9bfe72 100644
> --- a/arch/arm64/kvm/hyp/include/nvhe/mm.h
> +++ b/arch/arm64/kvm/hyp/include/nvhe/mm.h
> @@ -19,8 +19,10 @@ int hyp_back_vmemmap(phys_addr_t phys, unsigned long size, phys_addr_t back);
>  int pkvm_cpu_set_vector(enum arm64_hyp_spectre_vector slot);
>  int pkvm_create_mappings(void *from, void *to, enum kvm_pgtable_prot prot);
>  int pkvm_create_mappings_locked(void *from, void *to, enum kvm_pgtable_prot prot);
> -unsigned long __pkvm_create_private_mapping(phys_addr_t phys, size_t size,
> -					    enum kvm_pgtable_prot prot);
> +int __pkvm_create_private_mapping(phys_addr_t phys, size_t size,
> +				  enum kvm_pgtable_prot prot,
> +				  unsigned long *haddr);
> +int pkvm_alloc_private_va_range(size_t size, unsigned long *haddr);
>  
>  static inline void hyp_vmemmap_range(phys_addr_t phys, unsigned long size,
>  				     unsigned long *start, unsigned long *end)
> diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> index 5e2197db0d32..3cea4b6ac23e 100644
> --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> @@ -160,7 +160,23 @@ static void handle___pkvm_create_private_mapping(struct kvm_cpu_context *host_ct
>  	DECLARE_REG(size_t, size, host_ctxt, 2);
>  	DECLARE_REG(enum kvm_pgtable_prot, prot, host_ctxt, 3);
>  
> -	cpu_reg(host_ctxt, 1) = __pkvm_create_private_mapping(phys, size, prot);
> +	/*
> +	 * __pkvm_create_private_mapping() populates a pointer with the
> +	 * hypervisor start address of the allocation.
> +	 *
> +	 * However, handle___pkvm_create_private_mapping() hypercall crosses the
> +	 * EL1/EL2 boundary so the pointer would not be valid in this context.
> +	 *
> +	 * Instead pass the allocation address as the return value (or return
> +	 * ERR_PTR() on failure).
> +	 */
> +	unsigned long haddr;
> +	int err = __pkvm_create_private_mapping(phys, size, prot, &haddr);
> +
> +	if (err)
> +		haddr = (unsigned long)ERR_PTR(err);
> +
> +	cpu_reg(host_ctxt, 1) = haddr;
>  }
>  
>  static void handle___pkvm_prot_finalize(struct kvm_cpu_context *host_ctxt)
> diff --git a/arch/arm64/kvm/hyp/nvhe/mm.c b/arch/arm64/kvm/hyp/nvhe/mm.c
> index cdbe8e246418..670f11349070 100644
> --- a/arch/arm64/kvm/hyp/nvhe/mm.c
> +++ b/arch/arm64/kvm/hyp/nvhe/mm.c
> @@ -37,36 +37,60 @@ static int __pkvm_create_mappings(unsigned long start, unsigned long size,
>  	return err;
>  }
>  
> -unsigned long __pkvm_create_private_mapping(phys_addr_t phys, size_t size,
> -					    enum kvm_pgtable_prot prot)
> +/**
> + * pkvm_alloc_private_va_range - Allocates a private VA range.
> + * @size:	The size of the VA range to reserve.
> + * @haddr:	The hypervisor virtual start address of the allocation.
> + *
> + * The private virtual address (VA) range is allocated above __io_map_base
> + * and aligned based on the order of @size.
> + *
> + * Return: 0 on success or negative error code on failure.
> + */
> +int pkvm_alloc_private_va_range(size_t size, unsigned long *haddr)
>  {
> -	unsigned long addr;
> -	int err;
> +	unsigned long base, addr;
> +	int ret = 0;
>  
>  	hyp_spin_lock(&pkvm_pgd_lock);
>  
> -	size = PAGE_ALIGN(size + offset_in_page(phys));
> -	addr = __io_map_base;
> -	__io_map_base += size;
> +	/* Align the allocation based on the order of its size */
> +	addr = ALIGN(__io_map_base, PAGE_SIZE << get_order(size));
>  
> -	/* Are we overflowing on the vmemmap ? */
> -	if (__io_map_base > __hyp_vmemmap) {
> -		__io_map_base -= size;
> -		addr = (unsigned long)ERR_PTR(-ENOMEM);
> -		goto out;
> -	}
> +	/* The allocated size is always a multiple of PAGE_SIZE */
> +	base = addr + PAGE_ALIGN(size);
>  
> -	err = kvm_pgtable_hyp_map(&pkvm_pgtable, addr, size, phys, prot);
> -	if (err) {
> -		addr = (unsigned long)ERR_PTR(err);
> -		goto out;
> +	/* Are we overflowing on the vmemmap ? */
> +	if (!addr || base > __hyp_vmemmap)
> +		ret = -ENOMEM;
> +	else {
> +		__io_map_base = base;
> +		*haddr = addr;
>  	}
>  
> -	addr = addr + offset_in_page(phys);
> -out:
>  	hyp_spin_unlock(&pkvm_pgd_lock);
>  
> -	return addr;
> +	return ret;
> +}
> +
> +int __pkvm_create_private_mapping(phys_addr_t phys, size_t size,
> +				  enum kvm_pgtable_prot prot,
> +				  unsigned long *haddr)
> +{
> +	unsigned long addr;
> +	int err;
> +
> +	size += offset_in_page(phys);

I have the same comment as for the previous patch. Keep the ALIGN()
here in order to make the code readable (it is just an add+and on a
slow path).

> +	err = pkvm_alloc_private_va_range(size, &addr);
> +	if (err)
> +		return err;
> +
> +	err = __pkvm_create_mappings(addr, size, phys, prot);
> +	if (err)
> +		return err;
> +
> +	*haddr = addr + offset_in_page(phys);
> +	return err;
>  }
>  
>  int pkvm_create_mappings_locked(void *from, void *to, enum kvm_pgtable_prot prot)
> @@ -146,7 +170,8 @@ int pkvm_cpu_set_vector(enum arm64_hyp_spectre_vector slot)
>  int hyp_map_vectors(void)
>  {
>  	phys_addr_t phys;
> -	void *bp_base;
> +	unsigned long bp_base;
> +	int ret;
>  
>  	if (!kvm_system_needs_idmapped_vectors()) {
>  		__hyp_bp_vect_base = __bp_harden_hyp_vecs;
> @@ -154,13 +179,12 @@ int hyp_map_vectors(void)
>  	}
>  
>  	phys = __hyp_pa(__bp_harden_hyp_vecs);
> -	bp_base = (void *)__pkvm_create_private_mapping(phys,
> -							__BP_HARDEN_HYP_VECS_SZ,
> -							PAGE_HYP_EXEC);
> -	if (IS_ERR_OR_NULL(bp_base))
> -		return PTR_ERR(bp_base);
> +	ret = __pkvm_create_private_mapping(phys, __BP_HARDEN_HYP_VECS_SZ,
> +					    PAGE_HYP_EXEC, &bp_base);
> +	if (ret)
> +		return ret;
>  
> -	__hyp_bp_vect_base = bp_base;
> +	__hyp_bp_vect_base = (void *)bp_base;
>  
>  	return 0;
>  }

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.

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